Refrigerant system with intercooler and liquid/vapor injection
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Solution Overview
Problem
Refrigerant systems, particularly those using carbon dioxide, face high discharge temperatures due to high operating pressures and transcritical cycles, making the use of intercoolers and liquid/vapor injection less practical due to additional costs and limited benefits in conventional systems.
Innovation Solution
A refrigerant system with a multi-stage compressor incorporating an intercooler and liquid/vapor injection between compression stages, where the intercooler is subjected to ambient airflow and can be positioned in series or parallel with the heat rejecting heat exchanger, and the liquid/vapor injection is selectively activated based on environmental and thermal conditions to optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If an intercooler is added to cool refrigerant between compression stages, then discharge temperature is reduced and system reliability is improved, but device complexity and additional components are required
Solution Approach 1:
The intercooler is merged with the heat rejecting heat exchanger by positioning it in the airflow path of the outdoor fan. The same fan that provides airflow to the heat rejecting heat exchanger also provides cooling airflow to the intercooler, combining two heat exchangers into a single integrated thermal management system. This eliminates the need for separate cooling components for the intercooler.
Solution Approach 2:
The outdoor fan serves multiple functions: it provides airflow for the heat rejecting heat exchanger and simultaneously provides cooling airflow for the intercooler. This multi-functionality reduces the need for additional components and simplifies the overall system architecture.
2Reliability
If liquid/vapor injection is implemented to reduce discharge temperature, then compressor operational envelope is extended and reliability is improved, but device complexity and additional components are required
Solution Approach 1:
The liquid/vapor injection system is integrated with the existing expansion device and refrigerant circulation system. The injection utilizes the refrigerant already present in the system and the existing expansion capability, merging the injection function with the standard refrigerant distribution infrastructure rather than requiring entirely separate systems.
Solution Approach 2:
The system uses a portion of its own refrigerant circulation to provide cooling through liquid/vapor injection. The refrigerant that would otherwise go directly to the evaporator is partially diverted and expanded to provide injection cooling, allowing the system to serve its own cooling needs without external intervention.
3Productivity
If intercooler and liquid/vapor injection are both provided, then system efficiency and capacity are enhanced, but device complexity and cost increase
Solution Approach 1:
The system provides dynamic control of the liquid/vapor injection through a controllable expansion device, allowing the injection rate to be adjusted based on operating conditions. This dynamic adjustment optimizes system performance across different loads and environmental conditions while avoiding the complexity of multiple fixed-capacity injection systems.
Solution Approach 2:
The system changes the thermodynamic parameters of the refrigerant through controlled expansion and injection, adjusting the refrigerant's temperature and pressure to optimize heat transfer and system efficiency. This parameter control allows enhanced performance without requiring fundamentally different system architecture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution reduces compressor discharge temperature, enhances system efficiency and capacity, extends the operational envelope, and improves compressor reliability by allowing adjustable discharge pressure in transcritical cycles, while also providing additional cooling potential in the evaporator.
Implementation Method 1
an intercooler heat exchanger (or a so-called intercooler) between the compression stages to extend the operational envelope and/or improve system performance and reliability. In an intercooler, refrigerant flowing between the two compression stages is typically cooled by a secondary fluid.
Implementation Method 2
The intercooler is preferably positioned to be subjected to an airflow passing over a heat rejecting heat exchanger
Implementation Method 3
at least a portion of refrigerant leaving a heat rejecting heat exchanger is partially expanded in an auxiliary expansion device to an intermediate pressure and temperature and routed to a point between the compression stages where it is mixed with the refrigerant partially compressed in a lower compression stage
Implementation Method 4
a heat rejecting heat exchanger and a heat accepting heat exchanger. The heat rejecting heat exchanger is either a condenser for subcritical applications or a gas cooler for transcritical applications
Data Source
Figure 1~2
AI summary
A refrigerant system is provided with at least two sequential stages of compression. An intercooler is positioned intermediate the two stages. The refrigerant flowing through the intercooler is cooled by a secondary fluid such as ambient air. A vapor/liquid injection function is also provided for the refrigerant system. The intercooler function and the vapor/liquid injection function are selectively activated on demand depending on environmental conditions and thermal load in a conditioned space. This invention is particularly important for the CO2 refrigerant systems operating in the transcritical cycle.